Fast motion trick mode using non-progressive dummy predictive pictures

ABSTRACT

The invention concerns a method and system for performing a trick mode on a video signal containing a plurality of original pictures. The method includes the steps of selectively skipping at least one of the original pictures to convert the video signal to a trick mode video signal in response to a trick mode command and selectively inserting at least one dummy predictive picture in the trick mode video signal using field-based prediction. The method can also include the steps of monitoring the trick mode video signal in which the step of selectively inserting at least one dummy predictive picture in the trick mode video signal can be done if the bit rate of the trick mode video signal exceeds a predetermined threshold.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. 119(e) to ProvisionalApplication Ser. No. 60/334,914 filed on Oct. 23, 2001.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

(Not Applicable)

BACKGROUND OF THE INVENTION

1. Technical Field

The inventive arrangements relate generally to video systems and moreparticularly to video systems that record or play back digitally encodedvideo sequences.

2. Description of Related Art

Digital televisions (DTV) and high-definition televisions (HDTV) aregaining popularity in today's consumer electronics marketplace. Manypurchasers of these types of televisions also buy digital videorecorders or players, such as digital video disc (DVD) recorders orplayers, for purposes of viewing previously recorded programs orrecording their favorite programs. Notably, the combination of a DTV (oran HDTV) and a digital video recorder or player can be an integral partof a home theater entertainment system.

A digital video recorder or player typically contains a Moving PicturesExpert Group (MPEG) decoder to decode the digitally encoded multimediadata that is stored on the discs that the recorder or player plays. Ifthe digital video recorder or player is connected to a conventional(non-DTV or non-HDTV) television, the digitally encoded signal will bedecoded by the digital video recorder or players MPEG decoder beforebeing displayed on the conventional television. Significantly, however,many DTVs contain their own MPEG decoders. As such, if a digital videorecorder or player is connected to a DTV, the video signal read from thedisc is remotely decoded by the DTVs decoder. This configuration can bereferred to as a remote decoder arrangement.

There is, however, an important disadvantage in decoding digitallyencoded signals with a remote DTV decoder. Namely, it is very difficultto perform trick modes in this type of arrangement. A trick mode can beany playback of video in which the playback is not done at normal speedor in a forward direction. Oftentimes, a trick mode involves skipping anumber of pictures in a video signal such as during a fast motion trickmode. Skipping pictures in a video signal being transmitted to a remotedecoder can actually increase the average bit rate of the signal. As thebandwidth between the digital video recorder or player and the DTV islimited, performing a fast motion trick mode may cause the signal toexceed the maximum bit rate limit of the transmission channel.

For instance, in an MPEG video signal, there are three separate types ofdigitally encoded pictures: intra (I) pictures, predictive (P) picturesand bidirectional predictive (B) pictures. As is known in the art, I andP pictures contain relatively large amounts of encoded data, at leastwith respect to B pictures. During a fast motion trick mode, the firstpictures in a group of pictures (GOP) to be skipped are typically the Bpictures. As the B pictures are skipped, however, the average amount ofencoded data for the remaining pictures, or the average number of bitsper picture, in the GOP increases. Such a drawback can lead to bufferoverflow and the loss of pictures during the display of the trick modevideo signal.

In addition to the bit rate problem, there is another disadvantage todecoding video signals remotely: the repeated display of non-progressivepictures in such an arrangement can cause a vibration effect to appearin the display if the repeated pictures contain a moving object. Toexplain this drawback, a brief explanation of interlaced scanning iswarranted.

Many televisions employ the interlaced scanning technique. Under thisformat, the video signal is typically divided into a predeterminednumber of horizontal lines. During each field period, only one-half ofthese lines are scanned; generally, the odd-numbered lines are scannedduring the first field period, and the even-numbered lines are scannedduring the next field period. Each sweep is referred to as a field, andwhen fields are displayed per second, resulting in a rate of thirtyframes per second.

As a moving object moves across the screen in an interlaced scanningtelevision, each field will only display a portion of the moving object.This partial display occurs because a field only displays every otherhorizontal line of the overall picture. For example, for a particularfield n, only the odd-numbered horizontal lines are scanned, and theportion of the moving object that will be displayed in field n is theportion that is scanned during the odd-numbered horizontal line sweepfor field n. The next field, field n+1, is created {fraction (1/60)} ofa second later and will display the even-numbered horizontal lines ofthe picture. Thus, the portion of the moving object that is displayed infield n+1 is the portion that is scanned during the even-numberedhorizontal line sweep for field n+1. Although each field is temporallydistinct, the human eye perceives the sequential display of the fieldsas smooth motion due to the speed at which the fields are displayed.

If a viewer activates a trick mode, the trick mode video signal maycontain repeated pictures, pictures that were recorded under theinterlaced scanning format. For example, if the viewer initiates afreeze trick mode on a particular picture, then that picture can berepeatedly transmitted to and decoded and displayed at the DTVcontaining the remote decoder. The display of the repeated picture,however, is in accordance with the normal display of a non-progressivepicture, i.e, the fields that make up the non-progressive picture arealternately displayed.

If a moving object appears in the pictures recorded under the interlacedscanning format, each field will display the moving object in onespecific position. Thus, as these fields are alternately displayedduring the freeze trick mode, the moving object in the display rapidlymoves from one position in the display to another; in effect, the movingobject appears to vibrate. This vibration is created because theinterlaced fields are temporally distinct, and the moving object appearsin a different position for each field.

This problem is also present in DTVs that include a deinterlacer. As isknown in the art, a deinterlacer can construct complete frames from aninterlaced field. Thus, a deinterlacer can construct complete frames outof the fields that comprise the repeated non-progressive frame.Nevertheless, these complete frames constructed from the interlacedfields will also be displayed in an alternate fashion thereby creatingthe possibility of the vibration artifact. In addition, this vibrationeffect appears in not only a freeze trick mode but may also be presentin any other trick mode in which non-progressive pictures are repeated.Thus, it is desirable to eliminate the bit rate problem and thevibration artifact without increasing system costs or complexity.

SUMMARY OF THE INVENTION

The present invention concerns a method of performing a trick mode on avideo signal containing a plurality of original pictures. The methodincludes the steps of selectively skipping at least one of the originalpictures to convert the video signal to a trick mode video signal inresponse to a trick mode command and selectively inserting at least onedummy predictive picture in the trick mode video signal usingfield-based prediction. The method can also include the steps ofmonitoring the trick mode video signal and selectively inserting atleast one dummy predictive picture in the trick mode video signal if thebit rate of the trick mode video signal exceeds a predeterminedthreshold.

In one arrangement, the selectively inserting step can include the stepof selectively inserting at least a first dummy predictive picture inthe trick mode video signal using field-based prediction and subsequentdummy predictive pictures in the trick mode video signal usingframe-based prediction. The method can further include the step ofpredicting the at least first dummy predictive picture from a singlefield associated with a reference picture.

The reference picture can be an intra picture or a predictive picture.Additionally, the reference picture can be a non-progressive picture, aprogressive picture or a field picture. In another arrangement, theplurality of original pictures can be contained within a group ofpictures, and the reference picture that is used to predict the at leastfirst dummy predictive picture can be the last original picture in thegroup of pictures such that no other original pictures are predictedfrom the inserted dummy predictive pictures. Also, the trick mode can bea fast motion trick mode.

In one aspect of the invention, each of the plurality of originalpictures can contain a display indicator, and the method can furtherinclude the step of selectively modifying the display indicator of atleast a portion of the plurality of original pictures to reflect anintended display order when an original picture is skipped. The displayindicator can be a temporal reference field. Additionally, each temporalreference field can have an integer value, and the step of selectivelymodifying the temporal reference field of at least a portion of theplurality of original pictures can include the step of incrementallydecreasing by one the integer value of the temporal reference field eachtime an original picture is skipped.

In another aspect, the method can further include the step of decodingat least a portion of the trick mode video signal with a remote decoder.In yet another aspect, the plurality of original pictures can be in agroup of pictures and the method can further include the step ofskipping a remaining original picture each time a dummy predictivepicture is inserted in the trick mode video signal such that the lastpicture in the group of pictures is a dummy predictive picture and adesired playback speed is maintained following the insertion of thedummy predictive pictures.

The invention also concerns a method of performing a trick mode on avideo signal containing a plurality of original pictures. The methodincludes the steps of selectively skipping at least one of the originalpictures to convert the video signal to a trick mode video signal inresponse to a trick mode command and selectively inserting at least onenon-progressive dummy predictive picture in the trick mode video signalusing frame-based prediction.

The present invention also concerns a system for performing a trick modeon a video signal containing a plurality of original pictures. Thesystem includes a controller for reading data representative of thevideo signal from a storage medium and outputting the video signalcontaining the plurality of original pictures and a processor in whichthe processor is programmed to selectively skip at least one of theoriginal pictures to convert the video signal to a trick mode videosignal in response to a trick mode command and selectively insert atleast one dummy predictive picture in the trick mode video signal usingfield-based prediction. The system also includes suitable software andcircuitry to implement the methods as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a system that can perform a fast motiontrick mode using dummy predictive pictures in accordance with theinventive arrangements herein.

FIG. 2 is a flow chart that illustrates an operation of performing afast motion trick mode using dummy predictive pictures in accordancewith the inventive arrangements.

FIG. 3 illustrates a typical group of pictures structure in an MPEGvideo signal containing non-progressive pictures.

FIG. 4A illustrates one example of inserting dummy predictive picturesinto a trick mode video signal in accordance with the inventivearrangements.

FIG. 4B illustrates another example of inserting dummy predictivepictures into a trick mode video signal in accordance with the inventivearrangements.

FIG. 4C illustrates yet another example of inserting dummy predictivepictures into a trick mode video signal in accordance with the inventivearrangements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A system 100 for implementing the various advanced operating features inaccordance with the inventive arrangements is shown in block diagramform in FIG. 1. The invention, however, is not limited to the particularsystem illustrated in FIG. 1, as the invention can be practiced with anyother system capable of receiving a digitally encoded signal andtransferring that signal to a display device. In addition, the system100 is not limited to reading data from or writing data to anyparticular type of storage medium, as any storage medium capable ofstoring digitally encoded data can be used with the system 100.

The system 100 can include a controller 110 for reading data from andwriting data to a storage medium 112. The system 100 can also have asearching engine 114, a microprocessor 116, a transmission buffer 117and a display device 118. The searching engine 114 can contain suitablesoftware and circuitry for locating one or more particular types ofpictures in a video signal read from the storage medium 112. Control anddata interfaces can also be provided for permitting the microprocessor116 to control the operation of the controller 110 and the searchingengine 114. Suitable software or firmware can be provided in memory forthe conventional operations performed by the microprocessor 116.Further, program routines can be provided for the microprocessor 116 inaccordance with the inventive arrangements.

It should be understood that all or portions of the searching engine 114and the microprocessor 116 can be a processor 120 within contemplationof the present invention. Further, all or portions of the controller110, the searching engine 114, the microprocessor 116 and thetransmission buffer 117 can be a bitstream source 122 withincontemplation of the present invention. In one arrangement, the displaydevice 118 can contain its own decoder 119 for decoding all or a portionof any video signal read from the storage medium 112 and processed bythe bitstream source 122. In this particular arrangement, the decoder(not shown) in the bitstream source 122 typically does not decode thevideo signal read from the storage medium 112. This particularembodiment can be referred to as a remote decoder arrangement. It shouldbe noted, however, that the invention is not limited to thisarrangement, as the invention can be practiced in other suitablesystems.

In operation, the controller 110 can read a video signal containing aplurality of original pictures from the storage medium 112. Theseoriginal pictures can be non-progressive pictures, progressive picturesor field pictures. In one arrangement, if the microprocessor 116receives a trick mode command such as a fast motion command, then themicroprocessor 116 can signal the searching engine 114 to locate one ormore suitable original pictures in the trick mode video signal forpurposes of skipping such a picture. Once located, the searching engine114 can signal the microprocessor 116, and the microprocessor 116 canselectively skip at least one of the original pictures to convert thevideo signal to a trick mode video signal. The skipped pictures will notbe decoded nor will they be displayed during the trick mode.

In addition, during the trick mode command, the microprocessor 116 cansignal the searching engine 114 to locate another set of one or moresuitable original pictures for purposes of inserting dummy predictive(dummy P) pictures into the trick mode video signal. A dummy P pictureis a P picture that can be predicted from certain pictures in which thedummy P picture's motion vectors are set to zero and its residual signalis set to zero or not encoded.

Once a suitable original picture is located, the searching engine 114can signal the microprocessor 116, and the microprocessor 116 cangenerate a corresponding dummy P picture predicted from the locatedoriginal picture. The microprocessor 116 can then selectively insert atleast one of the corresponding dummy P pictures such that the dummy Ppicture is sent to the transmission buffer 117 and on to the displaydevice 118 and decoder 119. Inserting dummy P pictures in the trick modevideo signal can cause the overall bit rate of the signal to decrease,as dummy P pictures contain relatively small amounts of encoded data.

Generating dummy P pictures in this manner, i.e., when themicroprocessor 116 receives a trick mode command, is referred to asgenerating dummy P pictures “on-the-fly.” Alternatively, themicroprocessor 116 can generate dummy P pictures prior to the initiationof a trick mode command in which one or more of the dummy P pictures canbe stored in memory (not shown). Once the microprocessor 116 receives atrick mode command, the microprocessor 116 can retrieve one or more ofthe dummy P pictures from memory and insert them into the trick modevideo signal. In either arrangement, the dummy P pictures can be used torepeat original pictures such that the dummy P picture is transmitted tothe display device 118 and displayed.

In another aspect of the invention, the microprocessor 116 can monitorthe bit rate of the trick mode video signal. If the bit rate of thetrick mode video signal exceeds a predetermined threshold, then themicroprocessor 116, in conjunction with the searching engine 114, canperform the selectively inserting step discussed above in which at leastone dummy P picture can be inserted in the trick mode video signal.Also, the microprocessor 116 can insert dummy P pictures into the trickmode video signal that are constructed in which at least a first dummy Ppicture can be generated using a form of field-based prediction to avoidthe vibrating pictures problem. In one arrangement, subsequent dummy Ppictures can be predicted using frame-based prediction. Severaldifferent techniques will be discussed later. In another arrangement,the microprocessor 116 can also skip a remaining original picture when adummy P picture is inserted in the trick mode video signal to maintain adesired playback speed.

In another arrangement, the microprocessor 116 can modify certainportions of information contained within one or more of the plurality oforiginal pictures contained in the trick mode video signal to reflect anintended display order. This modification step can be performed whenoriginal pictures are skipped. The overall operation of the inventionwill be discussed in greater detail below.

Fast Motion Trick Mode Using Non-Progressive Dummy Predictive Pictures

FIG. 2 illustrates a method 200 that demonstrates one way to operate ina trick mode, such as a fast motion trick mode, using non-progressivedummy P pictures. In one arrangement, the invention can be practiced ina remote decoder arrangement. For purposes of the invention, a remotedecoder arrangement can be any system in which at least a portion of thepictures in a video signal can be decoded by a decoder that is externalto and not under the control of a bitstream source that is providing thepictures to the decoder.

As an example, the bitstream source can be an optical storage mediumplayer or recorder that reads multimedia data from an optical storagemedium and transfers this data over a transmission channel to a digitaltelevision, which contains its own decoder. It is understood, however,that the invention is not limited to this example or even a remotedecoder arrangement, as the invention can be practiced in any othersuitable system or arrangement.

At step 210, a video signal containing a plurality of original picturescan be read. The original pictures can be non-progressive pictures,progressive pictures or field pictures. At step 212, a trick modecommand can be received. For purposes of the invention, the trick modecommand can be any command in which one or more of the original picturesare to be skipped, including a fast motion command such as fast forwardor fast reverse. As shown at step 214, at least one of the originalpictures can be selectively skipped. This selective skipping of picturesconverts the video signal to a trick mode video signal.

In one arrangement, the first original pictures to be skipped can be Bpictures. Referring to FIG. 3, a typical group of pictures (GOP) 300containing non-progressive pictures in display order is shown. Thesubscript numbers indicate when each picture will be displayed—relativeto the other pictures in the GOP—at a normal playback speed. Thelowercase letter “t” can represent a top field, and the lowercase letter“b” can represent a bottom field. This GOP 300 can be one of many GOPsin a video signal. Although the invention is not limited to thisparticular GOP structure, the GOP 300 will serve to illustrate how afast motion trick mode can be performed. For example, if a fast forwardplayback of 3× is desired (1× represents normal playback), then all theB pictures in the GOP 300 can be skipped. Thus, for this particular GOP,only the picture I₂ and the P pictures will be transmitted and/ordecoded and displayed.

For a faster trick mode speed, some of the P pictures can be skipped,and at certain speeds, the entire GOP 300 (including picture I₂) may beskipped. If P pictures are to be skipped, those of skill in the art willrealize that it would be preferable to first skip the P pictures towardsthe end of the GOP. In this example, picture P₁₄ would be skipped firstand then picture P₁₁ would be skipped and so on. Skipping pictures inthis manner can preserve the proper decoding sequence necessary todecode those pictures that will be displayed during the trick mode.

In another embodiment, each of the plurality of original pictures cancontain a display indicator. As determined at decision block 216, if thedisplay indicators of these pictures are to be selectively modified, thedisplay indicator of at least a portion of the plurality of originalpictures can be selectively modified, as shown at step 218. Notably,modifying these display indicators can reflect an intended display orderof the plurality of original pictures when an original picture isskipped. If the display indicators are not to be modified, then themethod 200 can continue at step 220.

In one arrangement, the display indicator can be a temporal referencefield. A temporal reference field is typically a ten bit field locatedin the picture header of digitally encoded pictures. Some decoders relyon the temporal reference field to determine when a particular picturein a video signal will be displayed relative to other pictures in thevideo signal. This field normally has an integer value.

As an example, referring once again to FIG. 3, GOP 300 contains fifteenpictures. The subscript numbers for the pictures in the GOP 300 cancorrespond to the integer values for each respective picture's temporalreference field. For instance, the temporal reference field of pictureB₀, the first picture in the GOP, can have an integer value of zero. Thetemporal reference field of picture B₁, the next picture to bedisplayed, can have an integer value of one. Thus, the integer value ofthe temporal reference field for each subsequent picture to be displayedcan be higher by one, all the way to picture P₁₄, whose temporalreference field can have an integer value of 14. For convenience, thephrase “integer value of the temporal reference field” can also bereferred to as “integer value.”

When an original picture is skipped, however, the display orderaccording to the temporal reference fields of the original pictures isno longer valid. Accordingly, the integer value of the temporalreference fields of the original pictures that follow the skippedoriginal pictures can be modified to indicate a proper display order.

For example, if pictures B₉ and B₁₀ are skipped, then the integer valuesof those original pictures that follow can be decreased by a value oftwo. So, the integer value of the temporal reference field of pictureP₁₁ can be modified from eleven to nine, the integer value of thetemporal reference field of picture B₁₂ can be modified from twelve toten and so on. This modification process can continue until the end ofthe GOP 300 is reached and can ensure that the remaining pictures in theGOP 300 will be displayed in a proper order. Thus, each time an originalpicture in a GOP is skipped, the integer values of the temporalreference fields of the remaining pictures in that GOP that follow theskipped picture can be decreased by a value of one.

The step of modifying the integer values of the temporal referencefields of the non-skipped pictures in other GOPs in the trick mode videosignal can be carried out in accordance with these examples. It must benoted, however, that the invention is not limited to this particularexample, as other ways to modify the integer values of the relevanttemporal reference fields to reflect an intended display order can beperformed in any other suitable fashion. Moreover, it should be notedthat the invention is not limited to the use of a temporal referencefield, as any other suitable display indicator can be modified toreflect an intended display order in either of the embodiments discussedabove.

Referring back to method 200 in FIG. 2, at step 220, the bit rate of thetrick mode video signal can be monitored during the trick mode command.Monitoring the bit rate of the trick mode video signal may be necessaryduring a fast motion trick mode because, as mentioned earlier, skippingpictures may result in an increased average bit rate. In certain cases,this increased bit rate may exceed the maximum allowable bit rate forthe transmission channel that is carrying the video signal. For purposesof the invention, this maximum allowable bit rate for the transmissionchannel can be referred to as a predetermined threshold.

At decision block 222, it can be determined whether the bit rate of thetrick mode video signal has exceeded this predetermined threshold. Ifthe bit rate has not reached the predetermined threshold, then themethod 200 can continue at decision block 230. Referring back to step222, if the bit rate has exceeded the predetermined threshold, then oneor more dummy P pictures can be inserted in the trick mode video signal,as shown at step 224. In one arrangement, the dummy P pictures can bepredicted using field-based prediction, or, alternatively, the dummy Ppictures can be predicted using a combination of field-based and framebased prediction. That is, a dummy P picture can contain one or morefields, and each field can be predicted from another frame or fieldpicture, including any field that makes up a frame picture. As will beexplained below, inserting dummy P pictures into the trick mode videosignal can help lower the bit rate of to such a signal.

As previously noted, a dummy P picture is a P picture that can bepredicted from certain pictures in which the dummy P picture's motionvectors are set to zero and its residual signal is set to zero or notencoded. For example, in MPEG signals, a dummy P picture's discretecosine transform (DCT) coefficients can be set to zero or not encoded.As such, a dummy P picture contains very little information. A dummy Ppicture's primary purpose is to duplicate or repeat the picture, or afield of the picture, from which it was predicted using very few bits.Thus, as dummy P pictures are placed into a fast motion trick mode videosignal, the average number of bits per picture in the GOP decreasesthereby lowering the average bit rate.

A picture from which a dummy P picture is predicted is commonly referredto as a reference picture, and any number of the original pictures canbe reference pictures. In one arrangement, the reference picture can beeither an I picture or a P picture. In fact, those of ordinary skill inthe art will appreciate that dummy P pictures themselves can beconsidered to be reference pictures, as other dummy P pictures can bepredicted from them. In addition, the reference picture can be either anon-progressive picture, a progressive picture or a field picture.

To illustrate an example of the insertion of dummy P pictures in a trickmode video signal, attention is once again directed to the GOP 300 inFIG. 3. If all the B pictures are skipped and pictures P₁₄ and P₁₁ areskipped (a playback speed of 5×), then any number of dummy P picturescan be inserted into the trick mode video signal to help lower the bitrate. The first of these dummy P pictures can be predicted from eitherpicture I₂, P₅ or P₈ in accordance with the discussion below.

There are several preferred ways to insert dummy P pictures into thetrick mode video signal. Inserting dummy P pictures in agreement withthese preferred methods can lower the bit rate and can help control thevibrating pictures artifact without substantially degrading picturequality. FIG. 4A shows one such example.

As shown in trick mode GOP 400, two dummy P frame pictures can beinserted into the trick mode video signal (the lowercase “d” indicatesthat a P picture is a dummy P picture). In accordance with the inventivearrangements, the first dummy P frame picture can be predicted from areference picture that is the last original picture in a GOP such thatno other original pictures are predicted from the inserted dummy Ppictures. Here, for example, the first dummy P frame picture can bepredicted from reference picture P₈.

In addition, the fields that comprise the first dummy P frame picturecan be predicted from a single field associated with the referencepicture, in this case, field P_(8b) of picture P₈. Although illustratedas being predicted from the second field of the first dummy P framepicture, the fields of the second dummy P frame picture can be predictedfrom either one of the fields of the first dummy P frame picture. Infact, the fields of the subsequent dummy P frame pictures are notlimited to single field prediction from the previous dummy P framepicture. Nonetheless, because the first dummy P frame picture waspredicted using single field prediction, the fields of the second dummyP frame picture, as well as any subsequent dummy P pictures, can beduplicates of the field from which the first dummy P frame picture waspredicted.

Referring to FIG. 4B, another example of inserting dummy P pictures intoa trick mode video signal in accordance with the inventive arrangementsis illustrated. As shown in GOP 410 and similar to GOP 400 of FIG. 4A,the first dummy P frame picture can be predicted using singlefield-based prediction. Here, however, the subsequent dummy P picturescan be predicted using frame-based prediction. That is, each successivedummy P frame picture, following the first dummy P frame picture, can bepredicted from the previous dummy P frame picture using frame-basedprediction. For example, following the field-based prediction of thefirst dummy P frame picture, the fields of the second dummy P framepicture can be predicted from the first dummy P frame picture usingframe-based prediction.

Of course, the invention is not limited to these particular examples, asany suitable number of dummy P frame pictures predicted from one or moreother suitable reference pictures can be inserted into the trick modevideo signal. Moreover, each field of each dummy P frame picture can bepredicted from any suitable field of its corresponding referencepicture, and the invention is not limited to predicting the first dummyP frame picture from a single field associated with a reference picture.

Using this particular prediction scheme, however, in which the fields ofthe first dummy P frame picture are predicted from a single fieldassociated with a corresponding reference picture, particularly wherethe reference picture is the last original picture in the GOP, can helpcontrol the vibrating pictures artifact and provide a suitable picturedisplay in addition to keeping the bit rate of the signal at anacceptable level. Specifically, predicting the fields of the first dummyP frame picture from a single field of the reference picture if dummy Pframe pictures are used during a trick mode can produce a display inwhich a moving object appears in one specific position for each of thefields of the dummy P frame pictures to be displayed.

That is, if a moving object appears in the reference picture from whichthe first dummy P frame picture is predicted and the fields of the firstdummy P frame picture are predicted from a single field of thisreference picture, then each field of subsequent dummy P frame pictureswill include the moving object in the same position as it is located inthe single reference field. Accordingly, as the dummy P frame picturesare displayed during the trick mode, the moving object does not appearto vibrate.

Also, because the first dummy P frame picture is predicted from areference picture that is the last original picture in the GOP, thesingle field prediction will not degrade picture quality. If an originalpicture is predicted from a dummy P picture whose fields are predictedfrom a single field associated with a reference picture, such aprediction scheme may cause problems in the original picture andsubsequent original pictures because the dummy P pictures were notpredicted from a complete picture. Inserting dummy P pictures followingthe last original reference picture, however, can avoid this dilemma.

In addition to inserting dummy P frame pictures, dummy P field picturescan be inserted into the trick mode video signal in accordance with theabove discussion. These field pictures, by their very nature, can eachbe predicted from a single field of the preceding reference picture. Forpurposes of the invention and in view of the foregoing discussion, theterm “dummy P pictures” can include dummy P frame pictures and dummy Pfield pictures except where expressly indicated.

It is also understood that the invention is not limited to employingfield-based prediction when inserting dummy P pictures in a trick modevideo signal. For instance, if dummy P frame pictures are to beinserted, then the dummy P frame pictures can be predicted merely usingframe-based prediction. As an example, the first dummy P frame pictureto be inserted can be predicted from the entire frame of the referencepicture, even if the reference picture is a non-progressive picture.This type of prediction can permit dummy P frame pictures to be insertedanywhere in a GOP so long as such insertion is in accordance withrelevant compression format standards.

Referring back to the method 200 of FIG. 2, there are several othersteps that can be performed, if desired, to maintain a desired playbackspeed. Each time a dummy P picture is inserted in the trick mode videosignal, the playback speed decreases, which may not be desirable. Toovercome this drop in playback speed, a remaining original picture canbe skipped when a dummy P picture is inserted, as shown at decisionblock 226 and step 228. If no original pictures are to be skipped, themethod 200 can resume at step 222. The skipping of original pictures canbe conducted in a manner such that the last picture in the GOP is adummy P picture and the desired playback speed is maintained followingthe insertion of dummy P pictures.

FIG. 4C shows an example in accordance with step 230 of FIG. 2. Similarto GOP 400, GOP 420 is a GOP in which the B pictures and the last two Ppictures have been skipped. A first dummy P frame picture predictedfrom, for example, field P_(5b) of picture P₅ can be inserted into theGOP 420, and picture P₈ can be skipped (the dashed lines represent askipped or deleted picture). This one to one insertion/deletioncorrespondence can ensure that the intended trick mode speed ismaintained.

Referring back to the method 200 of FIG. 2, at decision block 222, itcan be determined whether the insertion of the first dummy P framepicture lowered the bit rate of the trick mode video signal below thepredetermined threshold. If it did not, a second dummy P frame picturecan be inserted into the trick mode video signal, as shown at step 224.The second dummy P frame picture can be predicted using any suitableprediction technique such as those discussed in relation to FIGS. 4A and4B. That is, the second dummy P frame picture can be generated usingfield-based prediction in which its fields are predicted from, forexample, the second field of the first dummy P frame picture.Alternatively, the fields of the second dummy P frame picture can bepredicted from the first dummy P frame picture using frame-basedprediction. This example is illustrated in GOP 430 of FIG. 4D.

To maintain the desired playback speed and as also shown in FIG. 4D,picture P₅ can be skipped. As such, the first dummy P frame picture canbe predicted from picture I₂. In accordance with the inventivearrangements, the fields of the first dummy P frame picture can bepredicted from, for example, the field I_(2b). Referring back to FIG. 2,the method 200 can resume at step 222 to ensure that the bit rate of thetrick mode video signal does not exceed the predetermined threshold.Once the bit rate has been reduced to an acceptable level, the method200 can continue at decision block 230, where it can be determinedwhether the trick mode is to continue. If yes, the method 200 can resumeat step 214. If not, then normal playback can resume at step 232. It isunderstood that the method 200 is not limited in this regard, as thedecision block 230 can be positioned at any other suitable location inthe method 200.

As shown in FIG. 4C, the number of inserted dummy P pictures can equalthe number of skipped original pictures, and these dummy P pictures canbe inserted in the GOP such that a dummy P picture is the last picturein the GOP. Strategically inserting dummy P pictures into the trick modevideo signal in such a way lowers the bit rate, maintains the intendedplayback speed and positions a dummy P picture as the last picture inthe GOP to prevent future prediction problems in the GOP. It isunderstood that the invention is not limited to this particular example,as other insertion sequences can be conducted in accordance with theinventive arrangements.

The insertion of dummy P pictures can also reduce the choppiness of thedisplay of a trick mode video signal, which can be particularlytroublesome at a very fast motion trick mode. For example, referringback to GOP 300 in FIG. 3, if a 15× playback is to be performed (eitherin a forward or a reverse direction), then only picture I₂ will bedecoded and displayed. This algorithm can also apply to any otherfifteen picture GOPs in the trick mode video signal. Thus, only the Ipictures in subsequent GOPs for a fast forward trick mode and precedingGOPs for a fast reverse trick mode will be decoded and displayed. Such adisplay, however, can be very choppy and may cause an uncomfortableviewing experience, as jumping from I picture to I picture at a highrate may be difficult to follow because of scene changes or suddenappearances and disappearances of objects in the display.

Continuing with the example, inserting one or more dummy P pictures intothe trick mode video signal after each I picture, however, can enhancethe display of the trick mode. For example, a number of dummy P picturespredicted from picture I₂ can be inserted into the trick mode videosignal. Such an insertion can be in accordance with the discussionrelating to the examples illustrated in FIGS. 4A and 4B to control thevibrating pictures artifact or any other suitable prediction scheme.

Because they are repeats of picture I₂, the dummy P pictures increasethe amount of time the information in picture I₂ is displayed therebyreducing the choppiness of the display. This insertion step can alsolower the average bit rate of the trick mode video signal, as, in thisexample, the signal will have a relatively high bit rate because only Ipictures are being transmitted. To maintain the desired playback speed,subsequent or previous GOPs can be skipped following the insertion ofthe dummy P pictures. It is understood that the invention is not limitedto this example, as this process can also apply to any other GOP,including twelve picture GOPs.

Although the present invention has been described in conjunction withthe embodiments disclosed herein, it should be understood that theforegoing description is intended to illustrate and not limit the scopeof the invention as defined by the claims.

1. A method of performing a trick mode on a video signal containing aplurality of original pictures, comprising the steps of: in response toa trick mode command, selectively skipping at least one of the originalpictures to convert the video signal to a trick mode video signal; andselectively inserting at least one dummy predictive picture in the trickmode video signal using field-based prediction.
 2. The method accordingto claim 1, further comprising the steps of: monitoring the trick modevideo signal; and wherein the step of selectively inserting at least onedummy predictive picture in the trick mode video signal is done if a bitrate of the trick mode video signal exceeds a predetermined threshold.3. The method according to claim 1, wherein said selectively insertingstep comprises the step of selectively inserting at least a first dummypredictive picture in the trick mode video signal using field-basedprediction and subsequent dummy predictive pictures in the trick modevideo signal using frame-based prediction.
 4. The method according toclaim 3, further comprising the step of predicting the at least firstdummy predictive picture from a single field associated with a referencepicture.
 5. The method according to claim 4, wherein the referencepicture is a picture selected from the group comprising an intra pictureand a predictive picture.
 6. The method according to claim 4, whereinthe reference picture is a picture selected from the group comprising anon-progressive picture, a progressive picture and a field picture. 7.The method according to claim 4, wherein the plurality of originalpictures is contained within a group of pictures and wherein thereference picture that is used to predict the at least first dummypredictive picture is the last original picture in the group of picturessuch that no other original pictures are predicted from the inserteddummy predictive pictures.
 8. The method according to claim 1, whereinthe trick mode command is a fast motion trick mode.
 9. The methodaccording to claim 1, wherein each of the plurality of original picturescontains a display indicator and the method further comprises the stepof selectively modifying the display indicator of at least a portion ofthe plurality of original pictures to reflect an intended display orderwhen an original picture is skipped.
 10. The method according to claim9, wherein the display indicator is a temporal reference field.
 11. Themethod according to claim 10, wherein each temporal reference field hasan integer value and the step of selectively modifying the temporalreference field of at least a portion of the plurality of originalpictures comprises the step of incrementally decreasing by one theinteger value of the temporal reference field each time an originalpicture is skipped.
 12. The method according to claim 1, furthercomprising the step of decoding at least a portion of the trick modevideo signal with a remote decoder.
 13. The method according to claim 1,wherein the plurality of original pictures is in a group of pictures andwherein the method further comprises the step of skipping a remainingoriginal picture each time a dummy predictive picture is inserted in thetrick mode video signal such that the last picture in the group ofpictures is a dummy predictive picture and a desired playback speed ismaintained following the insertion of the dummy predictive pictures. 14.In a remote decoder arrangement, a method of performing a trick mode ona video signal containing a plurality of original pictures, wherein eachof the plurality of original pictures contains a display indicator,comprising the steps of: in response to a trick mode command,selectively skipping at least one of the original pictures to convertthe video signal to a trick mode video signal; monitoring a bit rate ofthe trick mode video signal; selectively inserting at least one dummypredictive picture in the trick mode video signal using field-basedprediction if the bit rate exceeds a predetermined threshold; andselectively modifying the display indicator of at least a portion of theplurality of original pictures to reflect an intended display order whenan original picture is skipped.
 15. A method of method of performing atrick mode on a video signal containing a plurality of originalpictures, comprising the steps of: in response to a trick mode command,selectively skipping at least one of the original pictures to convertthe video signal to a trick mode video signal; and selectively insertingat least one non-progressive dummy predictive picture in the trick modevideo signal using frame-based prediction.
 16. A system for performing atrick mode on a video signal containing a plurality of originalpictures, comprising: a controller for reading data from a storagemedium and outputting the video signal containing the plurality oforiginal pictures; and a processor, wherein the processor is programmedto: in response to a trick mode command, selectively skip at least oneof the original pictures to convert the video signal to a trick modevideo signal; and selectively insert at least one dummy predictivepicture in the trick mode video signal using field-based prediction. 17.The system according to claim 16, wherein the processor is furtherprogrammed to: monitor the trick mode video signal; and selectivelyinsert at least one dummy predictive picture in the trick mode videosignal if the bit rate of the trick mode video signal exceeds apredetermined threshold.
 18. The system according to claim 16, whereinthe processor is further programmed to selectively insert at least afirst dummy predictive picture in the trick mode video signal usingfield-based prediction and subsequent dummy predictive pictures in thetrick mode video signal using frame-based prediction.
 19. The systemaccording to claim 18, wherein the processor is further programmed topredict the at least first dummy predictive picture from a single fieldassociated with a reference picture.
 20. The system according to claim19, wherein the reference picture is a picture selected from the groupcomprising an intra picture and a predictive picture.
 21. The systemaccording to claim 19, wherein the reference picture is a pictureselected from the group comprising a non-progressive picture, aprogressive picture or a field picture.
 22. The system according toclaim 19, wherein the plurality of original pictures is contained withina group of pictures and wherein the reference picture that is used topredict the at least first dummy predictive picture is the last originalpicture in the group of pictures such that no other original picturesare predicted from the inserted dummy predictive pictures.
 23. Thesystem according to claim 16, wherein the trick mode command comprises afast motion trick mode.
 24. The system according to claim 16, whereineach of the plurality of original pictures contains a display indicatorand the processor is further programmed to selectively modify thedisplay indicator of at least a portion of the plurality of originalpictures to reflect an intended display order when an original pictureis skipped.
 25. The system according to claim 24, wherein the displayindicator comprises a temporal reference field.
 26. The system accordingto claim 25, wherein each temporal reference field has an integer valueand the processor is further programmed to selectively modify thetemporal reference field of at least a portion of the plurality oforiginal pictures by incrementally decreasing by one the integer valueof the temporal reference field each time an original picture isskipped.
 27. The system according to claim 16, further comprising aremote decoder for remotely decoding at least a portion of the trickmode video signal.
 28. The system according to claim 16, wherein theplurality of original pictures is in a group of pictures and wherein theprocessor is further programmed to skip a remaining original pictureeach time a dummy predictive picture is inserted in the trick mode videosignal such that the last picture in the group of pictures is a dummypredictive picture and a desired playback speed is maintained followingthe insertion of the dummy predictive pictures.
 29. In a remote decoderarrangement, a system for performing a trick mode on a video signalcontaining a plurality of original pictures, wherein each of theplurality of original pictures contains a display indicator, comprising:a controller for reading data from a storage medium and outputting thevideo signal containing the plurality of original pictures; and aprocessor, wherein the processor is programmed to: in response to atrick mode command, selectively skip at least one of the originalpictures to convert the video signal to a trick mode video signal;monitor a bit rate of the trick mode video signal; selectively insert atleast one dummy predictive picture in the trick mode video signal usingfield-based prediction if the bit rate exceeds a predeterminedthreshold; and selectively modify the display indicator of at least aportion of the plurality of original pictures to reflect an intendeddisplay order when an original picture is skipped.
 30. A system forperforming a trick mode on a video signal containing a plurality oforiginal pictures, comprising: a controller for reading data from astorage medium and outputting the video signal containing the pluralityof original pictures; and a processor, wherein the processor isprogrammed to: in response to a trick mode command, selectively skip atleast one of the original pictures to convert the video signal to atrick mode video signal; and selectively insert at least onenon-progressive dummy predictive picture in the trick mode video signalusing frame-based prediction.